The PCNs affected were issued between April 1 and October 13 for 'moving traffic violations', in which security cameras captured driving misdemeanours on film and a council computer automatically issued tickets to the vehicles' owners through the post.

It was an appeal to the independent adjudicator - the Parking and Traffic Appeals Service (PTAS) - by 67-year-old motorist John Evans, of Rayners Lane, South Harrow, that exposed the fact that the council's notices did not meet the legal requirements.

The PTAS adjudicator ordered the authority to cancel the PCN after finding the correspondence was 'defective' because it did not mention how Mr Evans could argue against the ticket or that he had the right to view the evidence on which the authority was relying.

The council did not realise the potential consequences of the adjudicator's decision, issued on September 9, until the Observer contacted the authority on October 14.

Six days later, following legal advice, Harrow Council announced that the 3,400 outstanding PCNs were being withdrawn because they were based on the same illegal computer-generated template as used in Mr Evans' case.

However, the 9,380 drivers who paid the fines, having unknowingly received one of these flawed dispatches, will not get refunds.

Councillor Susan Hall (Conser-vative), deputy leader and portfolio holder for environmental services, said: "In retrospect, the wording on this specific ticket wasn't as clear as it could have been. We've taken fresh legal advice to ensure the new parking notice for parking offences captured on CCTV is absolutely correct. The error relates to a small number of tickets issued between April and mid-October this year. The vast majority of the tickets we issue are unaffected."

Mr Evans said: "There's no excuse. They have experts in the legal deparment being paid a lot of money to get things right. If the adjudicator, who is also an expert, can spot it, why didn't they?"